The standard technique of protecting high voltage circuitry from the environment and from internal arcing, due to the necessity to violate open air construction spacing rules while using compact construction techniques with high voltage levels, entails encapsulating the circuitry using an open potting shell or mold, pouring in liquid state epoxy or RTV rubber, vacuum dc-airing the material, and then curing the assembly at room temperature for a certain period of time. This traditional method requires many steps and much time to complete, and is thus not well suited for high volume, low cost assembly of high voltage circuit boards. Therefore, it would be highly desirable to have an encapsulation technique that would entail fewer steps, be more efficient and less expensive to perform, as well as be suitable for high volume low cost assembly of high voltage circuit boards.
High voltage connections require long tracking distances and the use of insulating material to prevent corona and electron leakage from the point of connection. This is most often done by deeply recessing an open contact point at the base of a long tunnel of insulating material to form the “female” contact, with the male contact being a long conductor point insulated by an appropriate material, except at the point of connection at the bottom of the tunnel. The common terminology for this is a “poke-home connection”. These connectors tend to be expensive and space consuming. Therefore, it would be highly desirable to have a connection tunnel that is integrated into the encapsulation over-molding material including a built-in contact or other typical conductive contact device, such as but not limited to, a conductive rubber slug.
The use of a conductive rubber slug to make an electrical contact is not new, however, it would be highly desirable to have a novel design which incorporates a metal “saddle” by which the slug is secured to the printed circuit board. This way, the saddle is assembled and soldered to the printed circuit board by normal surface mount assembly and soldering techniques, and the slug could then be pushed in place into the saddle by another normal assembly pick and place operation, saving time and expense. By this process the rubber slug is additionally encapsulated with a thin cross sectional area adjacent to the integrated poke-home connection tunnel creating a thin membrane surface on that side.
Often in Voltage high voltage work, surface mount components, suitable for high voltage operation, of a specific size and performance are not available, or if they are, they are dramatically more expensive than the conventional “thru-hole” counterpart. This is the case with a resistor used for high voltage regulation feedback. The use of axially leaded components with surface mount assembly techniques would normally require complex lead formation devices and special tape cavity carriers to allow for proper component alignment into the pick and place machinery prior to placement on the board. Therefore, it would be highly desirable to have a slot pre-cut into the printed circuit board where the resistor or any other axially or conventionally leaded component will mount in a recessed fashion to enable quick assembly and complete encapsulation over the component and printed circuit board.
Numerous innovations for encapsulating circuitry have been provided in the prior art that are described as follows. Even though these innovations may be suitable for the specific individual purposes to which they address, they differ from the present process as hereinafter contrasted. The following is a summary of those patents most relevant to the description at hand, as well as a description outlining the difference between the features of the present process of encapsulating high voltage circuitry with a connector contact means and those of the prior art.
U.S. Pat. No. 7,211,215 of Marcel Gerardus Antonius Tomassen et al. relates to a mold for encapsulating electronic components mounted on a carrier, comprising: of at least two mold parts displaceable relative to each other, at least one of which is provided with a recess, and feed means for encapsulating material, wherein at least one of the mold parts is provided with a runner which connects on one side to a wall of a mold part co-defining a mold cavity and connects on the other side to a side of the mold part remote from the mold cavity. The invention also relates to an encapsulating device of which such a mold forms parts, and to a method for encapsulating electronic components mounted on a carrier.
This patent describes a mold for encapsulating conventional electronic components mounted on a carrier but does not deal with the unique problems incurred with encapsulating high voltage circuitry or the incorporation of contact means within the encapsulating material or the use of a low pressure injection molding encapsulating technique.
U.S. Pat. No. 6,534,711 of Richard Stephen Pollack describes a package for encapsulating electronic components that has at least two chambers. Electronic components and modules within the chambers are interconnected by a lead frame extending between the two chambers. One chamber may surround the other chamber, or it may be adjacent the other chamber. The sidewall of one chamber may be higher than the sidewall of the other chamber. Each of the chambers may individually be filled with encapsulating material. Temporary connections to the lead frame may be made after one chamber is filled with encapsulating material, in an unfilled other chamber of the package, which is subsequently filled with encapsulating material. A portion of a lead frame may extend to the exterior of the package. Openings may be provided in an external surface of the package for making connections with external components. The electronic components may include an RF-transponder and a pressure sensor, and the package may be mounted within a pneumatic tire.
This patent describes a novel technique for packaging electronic circuit modules and components. It does not use an injection molding process or deal with the problems involved with high voltage circuitry or the innovative way of creating a slot pre-cut into the printed circuit board where the resistor or any other axially or conventionally leaded component will mount in a recessed fashion to enable quick assembly and complete encapsulation.
U.S. Pat. No. 6,531,083 of Mario A. Bolanos et al. describes a method and apparatus for encapsulating an integrated circuit die and lead frame assembly. A prepackaged sproutless mold compound insert is placed in a rectangular receptacle in a bottom mold chase. The receptacle is coupled to a plurality of die cavities by runners. Lead frame strip assemblies containing lead frames, integrated circuit dies, and bond wires coupling the lead frames and dies are placed over the bottom mold chase such that the integrated circuit dies are each centered over a bottom mold die cavity. A top mold chase is placed over the bottom mold chase and the mold compound package. The top mold chase has die cavities corresponding to those in the bottom mold chase. The mold compound insert is preferably packaged in a plastic film, which has heat sealed edges. The mold compound is forced through the package and heat seals during the molding process by the pressure applied by a rectangular plunger. The sproutless mold compound insert is packaged so that the mold compound will exit the packaging only where runners intersect the receptacle. The sproutless mold compound insert requires no alignment or cutting tools within the mold station. The plunger is applied using variable speed and pressure to control the rate the mold compound fills the cavities in the top and bottom mold chases, thereby avoiding voids in the completed packages and minimizing wire sweep of the bond wires of the integrated circuit assemblies.
This patent relates to the field of die and lead frame assembly of integrated circuits and to the encapsulation packaging using transfer-molding techniques which is a much slower process than the low pressure injection molding process and less adaptable to a rapid production. It does not incorporate the low-pressure injection molding process, the conductive rubber slug or the integrated connection tunnel.
U.S. Pat. No. 4,861,251 of Max Moitzger describes an apparatus for encapsulating selected portions of the printed circuit board in a pin grid array using transfer-molding techniques. In one embodiment for encapsulating only the top surface and side edges of the board, a vacuum is provided in the lower cavity to hold the edges of the bottom surface of the board flush against the mold plate. In a second embodiment for encapsulating all exposed surfaces of the board, the array pins are inserted in holes in the bottom of the cavity and supported by an adjustable block which positions the board in the cavity.
This patent describes an apparatus for encapsulating selected portions of conventional printed circuit boards but does not deal with the unique problems involved with a high voltage circuit board and does not include incorporating a means of connection into the encapsulation material.
None of the foregoing prior art teaches or suggests the particular unique features of encapsulating high voltage circuitry incorporating a connector contact means and thus clarifies the need for further improvements in the field of encapsulating high voltage components.
In this respect, before explaining at least one embodiment of the design in detail it is to be understood that the encapsulating high voltage circuitry incorporating a connector contact means is not limited in its application to the details of construction and to the arrangement of the components set forth in the following description or illustrated in the drawings. The process is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.